A negative resistance element involves a resonator and is useful in an application field of an electromagnetic wave oscillation element. Up to now, it has been proposed that an electromagnetic wave including at least a part of a frequency band from a millimeter waveband to a terahertz band (which is higher than or equal to 30 GHz and lower than or equal to 30 THz) (hereinafter, will be simply referred to as “terahertz wave”) can be generated by using the negative resistance element. As one of the configurations, NPL 1 discloses a monolithic oscillator obtained by integrating the negative resistance element and the resonator to each other on a substrate. Slot antennas are integrated to each other on a semiconductor substrate including the negative resistance element, and a resonator structure and a gain medium are constituted in a monolithic manner.
FIG. 9 illustrates the oscillator according to NPL 1. In this oscillator, the negative resistance element uses a resonant tunneling diode S-RTD 91 provided with a Schottky barrier on a collector side. The resonator is a slot antenna. The slot antenna is constituted by a metallic pattern 92 on the semiconductor substrate and provided with capacitances 93 and 94 in end parts. The oscillator according to NPL 1 is further provided with a rectifier diode 95.
Here, the rectifier diode 95 functions as a stabilization circuit configured to suppress a parasitic oscillation which becomes a problem in the oscillator using the negative resistance element. The parasitic oscillation refers to a parasitic oscillation in a frequency region on a lower frequency side than a desired oscillation frequency fosc. Since the above-described parasitic oscillation decreases an oscillation output in the oscillation frequency fosc, the presence of the stabilization circuit may be considered to be important for the oscillator using the negative resistance element.
In view of the above, according to NPL 1, to reduce the parasitic oscillation, the stabilization circuit having a low impedance from the viewpoint of the negative resistance element is arranged in a location within ¼ of a wavelength λosc corresponding to the oscillation frequency fosc towards a power supply side as viewed from the S-RTD 91. Specifically, the shunt rectifier diodes 95 are integrated as the stabilization circuit in a location within λosc/4 towards a power supply 96 side as viewed from the S-RTD 91. A resistance 97 corresponds to a total of an internal resistance of the power supply 96 and a resistance of an electric wire. In this manner, by decreasing an impedance on a side of the power supply that supplies a bias voltage in a frequency region that is higher than or equal to DC and lower than fosc, it is possible to reduce the parasitic oscillation.
The above-described stabilization circuit in the related art for the suppression of the parasitic oscillation is a circuit configured to attenuate an amplitude of the parasitic oscillation in the low-frequency region where the oscillation is not desired by using a diode or a resistor. In the oscillation element or the oscillator that oscillates the electromagnetic wave in the millimeter waveband or the terahertz band, since the frequency range of the above-described low-frequency region is relatively widened, the amplitude of the parasitic oscillation is to be attenuated across the extremely wide band. For that reason, the design may be complicated, or the oscillation at the desired frequency may also be attenuated.